This section illustrates useful background information without admission of any technique described herein representative of the state of the art.
Cellular networks or more accurately cellular telecommunications networks are presently a vital tool for modern societies. As a necessary condition, they need to be secured to avoid phone bill frauds and to secure communications against illegal interception of private calls and messages. To this end, telecommunications operators of modern cellular networks protect their subscribers with a host of different techniques that typically rely on digital signal processing.
To enable cellular terminal to start communications, the terminals need to attach to a network in a network attach or network registration process. In the network registration process, a cellular terminal exchanges signals to authenticate itself or more accurately its subscription, typically using a UICC which hosts a Universal subscriber identity module (USIM) application. Sometimes also R-UIM, ISIM, SIM card or SIM application or similar. In the network registration process, the terminal obtains from the network and the SIM access information such as a session key with which the terminal can subsequently communicate in the cellular network. The access information typically changes to prevent re-use of the access information by a possible illegal interceptor.
Encryption is a basic tool that is employed also in other types of digital cellular systems. Already GSM enabled encryption to mitigate illegal interception. The development of computer technology has subsequently made old encryption techniques more vulnerable, but also helped to enhance the security techniques used in cellular systems. For instance, wide-band CDMA (W-CDMA) was designed for stronger security by enabling also the network to authenticate itself to the terminals. In the W-CDMA, the subscriber identity is provided by a Universal Integrated Circuit Card (UICC) that runs a Universal Subscriber Identity Module (USIM). The USIM produces e.g. a session key based on a shared secret stored on the UICC, challenge and replay attack prevention codes received from the network and cryptographic algorithm that is enhanced over the one used in GSM. Also the authentication signaling is enhanced in the W-CDMA over GSM e.g. for protection against some man-in-the-middle attacks.
In parallel with the development of security methods for securing the communications in the cellular systems, there are also growing needs for developing the structure of cellular terminals. At present, most terminals contain an identity module slot in which a user can place and replace an identity module. There is also development towards software based identity modules that are not physically replaceable so as to enable over-the-air change of subscription and/or to prevent theft of the identity module from a terminal. Such software identity modules may be very useful e.g. for built-in vehicular communication systems so that their emergency reporting capabilities and possible burglar control systems could not be easily deactivated by removing an identity module. Those secure modules can be part of the cellular mode, a SoC (System on Chip), a trusted element or trusted platform. Those embedded secure elements are mainly used today for machine type communication, also known as M2M or Internet of Things communications.
Secure embedded elements prevent easy removal by thieves, but on the other hand various cellular communication enabled machines are expected to be in the market for 15-20 years (e.g. traffic lights, electricity and parking meters etc.). Moreover, increasing computational power may help attackers in their attempts to abuse cellular systems.